The present invention relates to an air cushion vehicle such as a Hovercraft vehicle, amphibious or not, equipped with an improved lift system which enables the supporting air to be transversely distributed automatically.
In order to define exactly the scope of application of the basic and essential characteristics included in its claims, it is necessary to define unmistakably what in this branch of engineering is understood by an air cushion vehicle or HOVERCRAFT vehicle and by its lift system.
A vehicle with these characteristics is that whose weight is totally or partially supported by the pressure of the air in an area limited vertically by elements of the same vehicle and the surface on which the former skims and horizontally by the vehicle's own means. Likewise, the lift system of the vehicle should be understood as the whole of the equipment or elements which enable it to be supported by the compressed air under it in a stable manner; also, apart from this primary function, the lift system can provide the vehicle with a series of desirable features, such as for example, low drag, minimum lift power, good platform stability, great directional stability, etc.
The aim of this invention is to develop an air cushion vehicle provided with a lift system which offers both roll and heave stability, easily adjustable between a very high value and another practically nil, which requires minimum supporting power, and which is also easy to execute.
In essence, the working of the lift system of a vehicle according to the present invention is based on the existence of a flexible keel, arranged below the hull of the vehicle, which divides the vehicle's air cushion into two longitudinal sections. When the vehicle heels the air outlet for the longitudinal section on the side of the vehicle approaching the surface closes and the flexible keel automatically directs the air from a distribution duct or internal channel, towards the longitudinal section or semichamber of the air cushion whose air outlet is closed. The air outlet for the longitudinal section on the side of the vehicle which is raised from the surface is fully opened and no air is directed from the internal channel towards the longitudinal section whose air oulet is open. The directing of the air by the flexible keel is performed with minimum loss of pressure due to the large air passage area which the flexible keel opens towards one of the longitudinal sections.
The roll stability of the vehicle is achieved by the difference in pressure between the two sections of the supporting chamber. Therefore, no contribution from the geometric configuration of the air cushion vehicle is necessary to obtain a sufficiently high stability value. The absence of a contribution by the geometric configuration to the stability of the air cushion vehicle makes it possible to achieve stability by using a valve which regulates the flow of supporting air between the two longitudinal sections.
The longitudinal stability of the vehicle is achieved by conventional methods, such as the geometrical arrangement of some of its elements, e.g., a certain angle of the bow skirt, or by a difference in air pressure between two air chambers one near each end of the vehicle with the pressure varying according to the longitudinal trim, or by a combination of both methods.
The characteristic features and originality of the vehicle provided with this supporting system, compared with others whose stability is also achieved by a difference in pressure, are due to the manner in which the flexible keel functions. The flexible keel makes it possible to distribute the air without any appreciable loss of pressure. Thus, the maximum pressure of the system can be practically equal to the minimum pressure, which is always the supporting pressure existing in the semichamber or air cushion. In addition, in accordance with the functioning of the flexible keel, the volume of the lift air flow necessary is of a minimum value for a given stability, because the internal air channel is not connected to the semichamber on the side which has its skirt separated from the surface, i.e., has its air outlet opened. When the vehicle heels the pressure in the longitudinal chamber on the side of the vehicle which approaches the surface increases. The increase in pressure occurs because the air outlet for that longitudinal section is closed. The closing of the air outlet also causes the flowrate in the longitudinal section to be practically reduced to zero. Hence, by having minimum pressure and flowrate values, the lift power required is also mimimum.
The lift system with which the vehicle is equipped is designed mainly to use lift fans with a characteristic pressure/flow curve having a considerable gradient (large dp/dq). The use of fans having a large dp/dq makes it possible to have the pressure in the rated working point of the fan practically equal to the air cushion or semichamber pressure. Another possible embodiment is to install fans with a characteristic pressure/flow curve having a smaller gradient or dp/dq, thereby creating a drop in pressure between the fan outlet and the semichamber, which is achieved by means of constricting the air passage. In any event, it should be stressed that fans having a large dp/dq usually provide better efficiency than fans having a smaller dp/dq.
The control of the roll and heave stability according to the present invention provides the following advantages. A simple valve suffices to regulate the flow of air to regulate the vertical stability easily and instantaneously. Through this regulation, the vertical accelerations of the vehicle can be controlled, which is translated into a greater platform stability without loss of roll stability. With this system, maximum regulation capacity is also obtained due to the virtual absence of any geometrical configuration contributing to the stability component.
The vehicle of the present invention has the further advantage of being able to control the vehicle roll simply, thereby improving its maneuvering and safety qualities.
A single valve is sufficient to control both vertical and transversal accelerations due to the manner in which the flexible keel functions. Indeed, if the pressure is the same in both air cushion longitudinal sections or semichambers the keel distributes the air equally to both semichambers. Closing the air flow valve from the fan to the keel has the effect of reducing the pressure in both semichambers, which is equivalent to a reduction in the lift force to a compensation of a purely vertical acceleration. If on the other hand, the acceleration produced is transversal or in roll, this means that there is a higher pressure in one of the air cushion semichambers, and hence the keel directs the air to that semichamber. A reduction in the air pressure therefore only effects that same semichamber.
The varied forms and embodiments which can be achieved by applying the basic principles of the present invention will be described in detail with the aid of the attached sheets of drawings, which are given by way of example.